Satellite antenna systems receive signals from satellites orbiting the earth. The satellite is equipped with an antenna system including a configuration of antenna feeds that receive the uplink signals and transmit the downlink signals to the Earth. Typically, the antenna system includes one or more arrays of feed horns, where each feed horn array includes an antenna reflector for collecting and directing the signals. Many satellite communications systems use the same antenna system and array of feed horns to receive the uplink signals and transmit the downlink signals. Combining satellite uplink signal reception and downlink signal transmission functions for a particular coverage area using a reflector antenna system requires specialized feed systems capable of supporting dual frequencies and providing dual polarization.
A dual polarized waveguide junction with one or two sets of single polarized side waveguide ports is a basic component of dual polarized dual frequency band antenna feed systems. This type of device is known to one skilled in the art as an ortho-mode transducer (OMT) or ortho-mode junction (OMJ). The OMT or OMJ in combination with each feed horn provide signal combining and isolation to separate the uplink and downlink signals.
An early example of a OMJ is disclosed in U.S. Pat. No. 3,731,235. The OMJ of this patent outlines a circular waveguide with a set of four symmetrical openings around the periphery of the waveguide.
A current example of an OMJ is disclosed in U.S. Pat. No. 6,566,976. The patent discloses a symmetric orthomode coupler for a satellite communication system. More specifically, it discloses a tapered orthomode coupler that allows for dual sense polarization for both transmission and reception frequency bands.
The current orthomode couplers are limited in their ability to provide an extended operational bandwidth and mode purity of the highest frequency signals. Thus, there is a need in the art to provide an orthomode coupler that extends the operational bandwidth and transfers the highest frequency signals through the OMJ with minimal modal distortion and low return loss. It is therefore an object of the present invention to provide such improved orthomode coupler.